One or more embodiments of the invention relate to a torque-limited attachment device, having a first head piece with at least one shaped element for the purpose of establishing a positive-fit connection to an attachment tool, and a second head piece which has at least one threading, wherein both head pieces are connected to each other, forming a predetermined breaking point which breaks at a limit torque between the two head pieces such that a first breakaway surface, the same being functionally assigned to the first head piece, and a second breakaway surface, the same being functionally assigned to the second head piece, are created, and wherein at least the second head piece and preferably the first head piece have a base material inside which has a corrosion-resistant surface coating.
Breakaway nuts or breakaway bolts having two heads are known, the same being connected to each other via a welded connection. When these nuts and/or bolts are affixed, a torque is applied to the first head piece by means of an attachment tool, wherein the torque is transferred via a connection to the second head piece at the beginning of the attachment process. When a prespecified limit torque is reached at the end of the attachment process, the first head piece shears off from the second head piece at the connection. The maximum torque applied to the second head piece is limited by this shearing.
For example, US 2002/076295 A1 discloses a breakaway nut. A breakaway bolt is known from GB1411151A.
For reasons of cost, breakaway nuts are frequently produced from a base material which is comparatively susceptible to corrosion. This base material is protected from corrosion by means of a treatment of the surface thereof. However, observations have shown that corrosion problems can occur during the use of such breakaway nuts in certain circumstances despite this surface treatment.